1. Field
The following description relates to a power amplifying apparatus having a spurious signal reduction function.
2. Description of Related Art
A power amplifying apparatus manufactured as a module is generally known as a power amplifier module (PAM). A PAM may amplify a radio frequency (RF) signal of an output of a transmitter and transmit the amplified RF signal to an antenna. Such a PAM may include switches and filters and a power amplifier (PA) that amplifies the RF signal to support various frequency bands.
The signal amplified by the PA may pass through the respective appropriate filters through a band selection switch (BSSW) and may be then transmitted to the antenna via an antenna switch module (ASM). In this example, the BSSW and the ASM may include an RF switch to select an appropriate band.
In order to significantly reduce an influence by a switched-off path other than a path selected by such an RF switch, the RF switch may use a negative voltage (VNEG) or VDD negative (−VDD).
As such, the negative voltage, for example, VNEG, used by the RF switch is applied to a gate and a body of the switch in the switched-off path to improve characteristics of the switch. In this example, the negative voltage is generated using an oscillator (OSC) and a charge pump (CP), the oscillator generates a clock signal, and the charge pump performs charging and discharging for a capacitor using the clock signal to generate the negative voltage, for example, VNEG.
In this example, a spurious signal generated along with the clock signal is introduced into the charge pump, the oscillator, and a power circuit, for example, a voltage regulator such as a low-dropout regulator (LDO) supplying operating power to the charge pump. For example, an LDO is a DC linear voltage regulator is that is able to regulate an output voltage even when a supply voltage is very close to the output voltage. As a result, there may be an issue in which the operating power becomes unstable due to spurious signals.
An amount of spurious signals as described above may not be high, and because a filter filtering a signal of a corresponding frequency is embedded in a frequency division duplex (FDD) mode using different frequencies, the spurious signals may not be a significant problem in FDD mode.
However, because a time division duplex (TDD) mode uses the same frequency for transmission, there is a potential issue when operating in TDD mode that the spurious signals of the charge pump may be generated, which may adversely affect the successful operation of the power circuit described above.
As an example, in an example PAM system, a controller controls an application of an appropriate bias to the power amplifier (PA) using a mobile industry processor interface (MIPI), and controls a selection of an appropriate band by applying a band selection signal to the BSSW so that an output signal of the power amplifier (PA) is provided to the filter of the appropriate band. In addition, the controller controls a switching operation of the BSSW by applying a positive voltage, for example, the LDO voltage, and the negative voltage, for example, VNEG, output by the charge pump to the BSSW for performing an on/off operation.
However, in such a PAM system, there may be an issue in which spurious signals, such as clock noise, corresponding to the operation frequencies of the oscillator and the charge pump, are generated along with an output of the power circuit such as an LDO, or the like as discussed above, and along with an output of the charge pump.
In addition, such spurious signals potentially appear in the output of the BSSW in various paths. In an example in which the spurious signal appears in a received band frequency, there is a potential issue in which the spurious signal is a factor that deteriorates sensitivity.